Naphthols are generally prepared from the corresponding isomeric isopropylnaphthalene hydroperoxides by the Hock process, from isomeric naphthalenesulfonic acids by alkali hydrolysis or from naphthylamines by acidic hydrolysis. Due to the necessity of using large excess of acid or alkali, as well as limitations in the availability and expensiveness of pure isomeric .alpha.- and .beta.-precursors, respectively, as well as the potentially carcinogenic nature of some of them, neither method is entirely satisfactory.
Only perfunctory studies have so far been reported on the direct hydroxylation of naphthalene. The reaction of aroyl peroxides with naphthalene via homolytic substitution giving mixtures of naphthols was reported by Davies, Hey and Williams (Journal Chemical Society (London), 1961, 3116. Friedel-Crafts type oxygenation of naphthalene with diisopropyl peroxydicarbonate gave a low yield of naphthols (Kovacic and Kurz, Journal or Organic Chemistry, Vol 31, 1966, 2001). In the reaction of 30% H.sub.2 O.sub.2 with naphthalene in HF in the presence of CO.sub.2 at superatmospheric pressure and at 4.degree.-11.degree. C., 30% .alpha.- and 9% .beta.-naphthol were obtained together with 17% 1,5-naphthalenediol and 35% of higher boiling and polymeric materials. (Vesely and Schmerling, Journal of Organic Chemistry, Vol. 35, 1970, 4028. This publication also reports that, in the absence of carbon dioxide, the product consisting only of high-melting, black, alkali soluble resinous material. High selectivity of .alpha.-naphthol is obtained with conventional acid systems, such as hydrogen fluoride in the absence of carbon dioxide, according to the present invention and contrary to the teachings of the Vesely et al. publication. None of these reactions are, thus, suitable for regioselectively producing .alpha.- or .beta.-naphthol.